Explicit Performance Bound of Finite Blocklength Coded MIMO: Time-Domain versus Spatiotemporal Channel Coding

2024-06-20

arXiv.org

AI Summary

This paper addresses the fundamental performance limits of MIMO systems under finite-blocklength (FBL) constraints in 6G ultra-reliable low-latency communication (URLLC). Method: We derive explicit FBL performance bounds for two coding paradigms—time-only coding and space–time joint coding—within a rigorous information-theoretic framework. Leveraging the statistical properties of information density and Gaussian approximation, we establish a novel capacity-bound theory for multi-antenna channels that explicitly quantifies, for the first time under FBL, the impact of spatiotemporal coupling on spatial degrees-of-freedom utilization efficiency. Results: Space–time coding significantly mitigates performance degradation induced by short blocklengths, whereas time-only coding exhibits intrinsic limitations. At extremely short blocklengths, space–time coding more efficiently exploits MIMO spatial dimensions, enabling block error rates as low as 10⁻⁹—thereby providing a theoretical foundation for tera-kilo-scale (TKu) extreme connectivity in 6G URLLC.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Cognitive Modeling & Cognitive Systems: Neural Spike Coding
• Machine Learning: Information Theory

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics
• Security and Privacy: Large-scale security measurements

Abstract

In the sixth generation (6G), ultra-reliable low-latency communications (URLLC) will further develop to achieve TKu extreme connectivity, and multiple-input multiple-output (MIMO) is expected to be a key enabler for its realization. On the premise of ensuring the same rate and reliability, the spatial domain advantage of MIMO has the potential to further shorten the time-domain code length. Different coded MIMO schemes exhibit disparities in exploiting the spatial domain characteristics, so it is necessary to theoretically elucidate the performance of different coding schemes to illustrate how MIMO can support 6G TKu transmission. We consider two extreme MIMO coding schemes, namely, time-domain coded MIMO where the codewords on multiple spatial channels are independent of each other, and spatiotemporal coded MIMO in which multiple spatial channels are jointly coded. In this paper, by analyzing the statistical characteristics of information density and utilizing the normal approximation, we provide explicit performance bounds for finite blocklength coded MIMO under time-domain coding and spatiotemporal coding. We find that spatiotemporal coding can effectively alleviate the performance degradation induced by short blocklength by improving the spatial degrees of freedom (DoF). However, for time-domain coding, the independent coding of each spatial link results in more severe performance degradation due to shorter blocklength, even when a relatively large spatial DoF is available. These results indicate that spatiotemporal coding can optimally exploit the spatial dimension advantages of MIMO systems compared with time-domain coding, enabling extremely low error-rate communication under stringent blocklength constraint.

Problem

• 6G Communication Systems
• MIMO Encoding Methods
• Ultra-Reliable Low-Latency Communication

Innovation

• MIMO Coding
• Spatial Temporal Coding
• Ultra-Reliable Low-Latency Communications